1. Field of the Invention
The present invention relates to a process for producing a thermoplastic resin composition.
2. Description of the Related Art
A thermoplastic resin, especially a high heat-resistant thermoplastic resin called engineering resin is broadly used as a molding material for various products and parts, such as machine parts, household electric appliances, communication apparatuses, OA parts, automobile parts, and leisure goods. In recent years, for the products and parts, downsizing, lightening and performance-elevating are more and more required. Following this, more light-weighted thermoplastic resins have been required as the materials with maintaining their properties as much as possible.
As a means for weight-lightening of a thermoplastic resin, i.e., lowering of specific gravity, methods of compounding hollow spheres have been known. Thermoplastic resin compositions compounded hollow spheres are described in JP-A 53-121851, JP-A 58-93759, JP-A 64-74258, etc. These compositions are usually manufactured with pelletizing by melt processing extrusion.
However, by the usual melt processing extrusion method, hollow spheres may be fractured in a considerable rate due to shear forces by melt-kneading. Thus, it has been difficult to obtain a composition of low specific gravity.
The object of the present invention is to solve the above-mentioned problem and to provide a process for producing a thermoplastic resin composition of low specific gravity containing hollow spheres by a melt processing extrusion method.
As a result of extensive studies, the present inventors have found that the above problems are solved by supplying a thermoplastic resin and hollow spheres to the extruder in a specific ratio, with using a specific melt processing extruder, thus completed the present invention.
Namely, the present invention relates to a process for producing a thermoplastic resin composition, wherein a melt-kneading extruder equipped with a screw is used and the extruder has an upper stream side supplying portion at the upper stream part of the extrusion direction, and a lower stream side supplying portion at the lower stream part from said upper stream side supplying portion, and the ratio (L/D) of the distance (L) between said upper stream side supplying portion and said lower stream side supplying portion to the diameter (D) of a screw is 4-30 (L and D are the same scale units); and under screw rotation, a thermoplastic resin having a specific gravity of 1.10 or more is supplied from the upper stream side supplying portion, and hollow spheres in an amount of 2-50 parts by weight based on 100 parts by weight of the thermoplastic resin are supplied from the lower stream side supplying portion.